The Football Association is being urged to commit Sir Alex Ferguson to an official agreement that he will curtail his criticism of referees. Alan Leighton, the national secretary of the referees' union, Prospect, wants Ferguson to pledge that he will stop being so outspoken after the Manchester United manager admitted a charge of improper conduct for his condemnation of Alan Wiley as not being physically fit enough to officiate in the Premier League.

Ferguson has requested a personal hearing at which he will apologise again for accusing Wiley of deliberately booking players because he needed a rest during United's 2-2 draw with Sunderland on 3 October. No date has been set but Leighton wants the FA to make an example of Ferguson by imposing a significant ban.

"We welcome the fact that he [Ferguson] has admitted his guilt and hope he will now dedicate himself to furthering the Respect agenda," he said. "If I was someone on the [FA disciplinary] panel I might be asking him for a commitment not to do the same thing again. It's his prerogative to request a personal hearing and it's up to the FA now to decide what punishment to give him."

Ferguson was also critical of Andre Marriner's performance in United's 2-0 defeat at Liverpool on Sunday but Leighton believes referees are getting more credit from other managers. "We have noticed that some of the managers are now discussing the referee's performances in more measured tones and in a constructive way," he added.